At what percentage above the cost price must an article be marked so as to gain 8% after allowing the customer a discount of 10%?

The article must be marked 20% above cost.

Take the cost price = 100; an 8% gain needs selling price = 108.

A 10% discount means SP = 0.9 x marked price.

0.9 x MP = 108, so MP = 108 / 0.9 = 120.

Mark-up = 120 - 100 = 20% above cost.